§ 27-700 Allowable axial load.
AC § 27-700
The allowable axial load on a pile shall be the least value permitted by consideration of the following factors (for battered piles, the axial load shall be computed from the resultant of all vertical loads and lateral forces occurring simultaneously): 1. The capacity of the pile as a structural member.
2.The allowable bearing pressure on soil strata underlying the pile tips.
3.The resistance to penetration of the piles, including resistance to driving, resistance to jacking, the rate of penetration, or other, equivalent criteria as established in this section.
4.The capacity as indicated by load test, where load tests are required.
5.The maximum loads prescribed in subdivision (e) of this section.
(a)The capacity of the pile as a structural member.
(1)EMBEDDED PORTION OF THE PILE. The compressive stress on any cross section of a pile produced by that portion of the design load that is considered to be transmitted to that section shall not exceed the allowable values for the construction materials as established in table 11-3. The tensile stress shall not exceed the values established in subchapter ten of this chapter for like material.
(2)PORTION OF THE PILE THAT IS NOT EMBEDDED. That portion of any pile that is free standing in air or water shall be designed as a column in accordance with the provisions of subchapter ten of this chapter, fixed at a point five feet below the soil contact level in class 8-65 material or better and ten feet below in any other material. The conditions of lateral and rotational restraint offered by the pile cap shall be considered in determining the equivalent unbraced length.
(3)LOAD DISTRIBUTION ALONG EMBEDDED PORTION OF THE PILE. The portion of the design load acting on any cross-section of a pile may be determined by analysis, considering time dependent changes in distribution of the load. As an alternative method for the purposes of this section, it may be assumed that: a. For piles embedded forty feet or more in materials of class 10-65 or better, or in controlled fills, and bearing on or in materials of classes 1-65 to 5-65: seventy-five per cent of the load shall be assumed to be carried by the tip. For shorter piles, with similar conditions of embedment and bearing, one hundred per cent of the load shall be assumed carried by the tip. b. For piles embedded in materials of class 10-65 or better, or in controlled fills, and bearing on or in materials of classes 6-65 to 10-65 (or controlled fills): the full load shall be assumed to act at a cross section located at two-thirds of the embedded length of the pile measured up from the tip. Where tapered piles are used, the stress at all sections of the pile shall be determined on the basis that the full load acts at a location as described above and that one-third of the full load acts at the tip. The stresses so computed shall not exceed the allowable values in table 11-3. c. For conditions not covered in subparagraphs a and b of this paragraph three the provisions relating to analysis shall apply. TABLE 11-3Allowable Compressive Stress for Pile Materials Pile MaterialAllowable Compressive Stress ConcreteConcrete – The provisions of Reference Standard RS 10-3 relating to short compression members shall apply. For working stress design use 0.25 f'c. For ultimate strength design use minimum eccentricity of 5 per cent, phi = 0.70 (phi = 0.75 where a permanent metal shell having a minimum wall thickness of 1/8 inch is used), and load factors as specified in Reference Standard RS 10-3. The above provisions shall be deemed applicable to reinforced and unreinforced sections. For unreinforced sections use Ds = D and d = t (symbols refer to those used in Reference Standard RS 10-3).Reinforcing steel – 0.40fy but not greater than 30,000 psi. (The provisions of article five of subchapter ten of this chapter relating to ties, spirals, and percentages of reinforcing steel for reinforced concrete compression members shall apply.)TimberSee timber piles (section 27-707 of article eight of this subchapter)SteelH piles – 0.35fy, with fy not to be taken as greater than 36,000 psi. Minimum thickness of metal shall be 0.40. Pipe piles, shells for cast-in place concrete piles and shells of pipe sections used in caisson piles: 0.35fy, (fy not to be taken as greater than 36,000 psi.) for thickness of 1/8 in. or more. Metal thinner than 1/8 in. shall not be considered as contributing to the structural strength of the pile section. Core sections for caisson piles: 0.50fy with fy not to be taken as greater than 36,000 psi. Note for Table 11-3: f'c = 28 day compressive strength of concrete. fy = Minimum specified yield strength of steel.
(b)Allowable bearing pressure on soil strata underlying the pile tips.
(c)Capacity as indicated by resistance to penetration. Where subsurface investigation, as described in article two of this subchapter, or general experience in the area, indicates that the soil that must be penetrated by the pile consists of glacial deposits containing boulders, or fills containing riprap, excavated detritus, masonry, concrete, or other obstructions in sufficient numbers to present a hazard to the installation of the piles, the selection of type of pile and penetration criteria shall be subject to the approval of the commissioner but in no case shall the minimum penetration resistance be less than that stipulated in Tables 11-4 and 11-5. Table 11-4Minimum Driving Resistance and Minimum Hammer Energy forSteel H-Piles, Pipe Piles, Precast and Cast-in-Place ConcretePiles and Composite Piles (other than timber) Minimum Driving Resistance a, c, e Pile Capacity (tons)Hammer b Energy (ft. lbs.)Friction Piles (blows/ft.)Piles Bearing on Hardpan (Soil Class 5-65) (blows/ft.)Non- Displacement Piles Bearing on Decomposed Rock (Soil Class 4-65) (blows/ft.)Displacement Piles Bearing on Decomposed Rock (Soil Class 4-65) (blows/ft.)Piles Bearing on Rock (Soil Classes 1-65, 2-65, & 3-65)Up to 20 15,00019,00024,000191511191511482716482716 30 15,00019,00024,000302318302318724026724026 40 15,00019,00024,000443224503630965334965334 50 15,00019,00024,00032,00072493524965437251208060401208060405 Blows per 1/4 inch (Minimum hammer energy of 15,000 ft. lbs.)60 15,00019,00024,00032,00096634430 240150100502401501005070 & 80 19,00024,00032,000 5 Blows per 1/4 inch (Minimum hammer energy of 15,000 ft. lbs.)5 Blows per 1/4 inch (Minimum hammer energy of 19,000 ft. lbs.) 100 Over 100 Notes for Table 11-4: a Final driving resistance shall be the sum of tabulated values plus resistance exerted by non-bearing materials. The driving resistance of non-bearing materials shall be taken as the resistance experienced by the pile during driving, but which will be dissipated with time and may be approximated as described in subparagraph a of paragraph one of subdivision (c) of this section. b The hammer energy indicated is the rated energy. c Sustained driving resistance – where piles are to bear in soil classes 4-65 and 5-65, the minimum driving resistance shall be maintained for the last six inches, unless a higher sustained driving resistance requirement is established by load test. Where piles are to bear in soil classes 6-65 through 10-65, the minimum driving resistance shall be maintained for the last twelve inches unless load testing demonstrates a requirement for higher sustained driving resistance. No pile need be driven to a resistance to penetration (in blows per inch) more than twice the resistance indicated in this table, nor beyond the point at which there is no measurable net penetration under the hammer blow. d The tabulated values assume that the ratio of total weight of pile to weight of striking part of hammer does not exceed 3.5. If a larger ratio is to be used, or for other conditions for which no values are tabulated, the driving resistance shall be as approved by the commissioner. e For intermediate values of pile capacity, minimum requirements for driving resistance may be determined by straight line interpolation. TABLE 11-5Minimum Driving Resistance and Hammer Energyfor Timber Piles Pile Capacity (tons)Minimum Driving Resistance (blows-in.) to be added to driving resistance exerted by non-bearing materials 1,3,4Hammer Energy (ft. – lbs.)2Up to 20Formula in Note4 shall apply 7,500-12,000 Over 20 to 25 9,000-12,000 14,000-16,000 Over 25 to 3012,000-16,000 (single-acting hammers) 15,000-20,000 (double-acting hammers) Greater than 30 Notes for Table 11-5: 1 The driving resistance exerted by non-bearing materials is the resistance experienced by the pile during driving, but which will be dissipated with time and may be approximated as described in subparagraph a of paragraph one of subdivision (c) of this section. 2 The hammer energy indicated is the rated energy. 3 Sustained driving resistance. Where piles are to bear in soil classes 4-65 and 5-65, the minimum driving resistance shall be maintained for the last six inches, unless a higher sustained driving resistance requirement is established by load test. Where piles are to bear in soil classes 6-65 thru 10-65, the minimum driving resistance measured in blows per inch shall be maintained for the last twelve inches unless load testing demonstrates a requirement for higher sustained driving resistance. No pile need be driven to a resistance to penetration (in blows per inch) more than twice the resistance indicated in this table nor beyond the point at which there is no measurable net penetration under the hammer blow. 4 The minimum driving resistance shall be determined by the following formula: P = 2WhH or P = 2E s + 0.1 s + 0.1 where: P = Allowable pile load in pounds. Wp = Weight driven in pounds. Wh = Weight of striking part of hammer in pounds. H = Actual height of fall of striking part of hammer in feet. E = Rated energy delivered by the hammer per blow in foot lbs. s = Penetration of pile per blow, in inches, after the pile has been driven to a depth where successive blows produce approximately equal net penetration. The value Wp shall not exceed three. Wh (1) PILES INSTALLED BY USE OF STEAM-POWERED, AIR-POWERED, DIESEL-POWERED OR HYDRAULIC IMPACT HAMMERS. a. The minimum required driving resistance and the requirements for hammer energies for various types and capacities of piles are given in tables 11-4 and 11-5. To obtain the required total driving resistance, the indicated driving resistances shall be added to any driving resistance experienced by the pile during installation, but which will be dissipated with time (resistance exerted by non-bearing materials or by materials which are to be excavated). For purposes of this section, the resistance exerted by non-bearing materials may be approximated as the resistance to penetration of the pile recorded when the pile has penetrated to the bottom of the lowest stratum of nominally unsatisfactory bearing material (class 11-65, but not controlled fill) or to the bottom of the lowest stratum of soft or loose deposits of class 9-65 or 10-65 but only where such strata are completely penetrated by the pile. The provisions of articles nine and ten of this subchapter shall also apply. b. Alternate for similitude method. The requirement for installation of piling to the penetration resistances given in tables 11-4 and 11-5 will be waived where the following five conditions prevail: 1. The piles bear on, or in, soil of class 5-65 through class 10-65.
6.Where the structure of the building or the spacing and length of the piling is such as to cause the building and its foundation to act as an essentially rigid body, the building piles may be driven to length and/or penetration into the bearing stratum without regard to penetration resistance, subject to the requirement of clause five of this subparagraph, relating to submission of report.
(4)LOAD TEST PROCEDURES. Before any load test is made, the proposed apparatus and structure to be used in making the load test shall be satisfactory to the commissioner and when required by him or her, all load tests shall be made under the commissioner's surveillance or that of his or her representative. A complete record of such tests shall be filed with the commissioner. a. Areas of the foundation site within which the subsurface soil conditions are substantially similar in character shall be established. In addition, for friction piles bearing on, or on, soil materials of class 6-65, or poorer, the uniformity of each such area shall be verified by installing at least three penetration-test piles, distributed over the area. Continuous records of penetration resistance shall be made for such piles. If the records of penetration resistance are not similar or are not in reasonable agreement with the information obtained from the borings, the assumed areas of similar subsurface conditions shall be modified in accordance with the information derived from the penetration-test piles and additional penetration-test piles shall be installed as required to verify the uniformity of such areas. b. For piles installed by jacking or other static forces or by impact hammer, one load test shall be conducted in each area of uniform conditions, but not less than two typical piles for the entire foundation installation of the building or group of buildings on the site, and not less than one pile for each fifteen thousand square feet of the area of the building wherein said piles are to be used shall be load tested. For piles installed by use of vibratory hammers, one comparison pile shall be installed and one index pile shall be load tested in each area of uniform conditions, but not less than two index piles shall be tested for the entire foundation installation of the building or group of buildings on the site, nor less than one index pile be tested for every seventy-five hundred square feet of pile foundation area. For piles whose capacity is determined on the basis of similitude, the provisions of subparagraph b of paragraph one of subdivision (c) of this section shall apply. c. The load test shall be conducted by a method that will maintain constant load under increasing settlement. Settlement observations shall be made by means of dial extensometers. The extensometers shall provide readings to the nearest one one-thousandth of an inch. In addition, settlement observations shall be taken using an engineer's level reading to one one-thousandth of a foot, properly referenced to a well-established benchmark.
1.Test loads shall be applied by direct weight or by means of a hydraulic jack. The loading platform or box shall be carefully constructed to provide a concentric load on the pile. If direct weight is employed, the loading increments shall be applied without impact or jar. The weight of the loading platform or box shall be obtained prior to the test and this weight shall be considered as the first increment of load. If a hydraulic jack is employed, facilities for maintaining each increment of desired load constant under increasing settlement shall be provided. The gauge and the jack shall be calibrated as a unit for each project.
(5)FOUNDATION PILES. Except as provided in clause six of subparagraph b of paragraph one of subdivision (c) of this section, all building piles within the area of influence of a given load-tested pile of satisfactory performance, shall be installed to the same or greater penetration resistance (or static load) as the successful load-tested pile. The same equipment (or heavier equipment of the same type) that was used to install the load-tested pile shall be used to install all other building piles, and the equipment shall be operated identically. Also all other piles shall be of the same type, shape, external dimension, and equal or greater cross section as the load-tested pile. All building piles within the area of influence represented by a given satisfactory load-tested pile shall bear in, or on the same bearing stratum as the load-tested pile. For friction piles where the actual pile lengths vary more than fifty per cent from that of the test pile, the commissioner may require investigation to determine the adequacy of the piles.
(6)PILE GROUPS. When the commissioner has reasons to doubt the safe load sustaining capacity of pile groups, he or she may require at the expense of the owner, group load tests up to one hundred fifty per cent of the proposed group load.
(7)"CASING-OFF." Any temporary supporting capacity that the soil might provide to the pile during a load test, but which would be dissipated with time, shall be obviated by "casing-off" or by other suitable means. For purposes of this section, temporary supporting capacity shall include the resistances offered by any strata of nominally unsatisfactory bearing materials (class 11-65, other than controlled fill) or of soft or loose deposits of class 9-65 or 10-65 that are completely penetrated by the pile, or any resistance offered by granular soils that will be dissipated by reason of vibration.
(e)Maximum loads.
(f)Combination of loads. The provisions of section 27-594 of subchapter ten of this chapter shall apply.
